A water-soluble and "self-assembled" polyoxometalate as a recyclable catalyst for oxidation of alcohols in water with hydrogen peroxide

Article abstract of DOI:10.1021/ja0344821

We have demonstrated that a simply prepared water-soluble polyoxometalate, Na₁₂[WZnZn₂(H₂O)₂(ZnW₉O₃₄)₂], synthesized from readily available zinc and tungsten salts in the presence of nitric acid, is an effective catalyst for selective alcohol oxidation with hydrogen peroxide in biphasic (water-alcohol) reaction media. Experiments have shown that the "self-assembled" catalyst in its mother liquor was as active as the isolated catalyst. The aqueous catalyst solution is easily separated from the water-insoluble products and can be recycled without loss in activity or selectivity. Copyright

Full text of DOI:10.1021/ja0344821

Published on Web 04/10/2003
A Water-Soluble and “Self-Assembled” Polyoxometalate as a Recyclable
Catalyst for Oxidation of Alcohols in Water with Hydrogen Peroxide
†
‡
,†
Dorit Sloboda-Rozner, Paul L. Alsters, and Ronny Neumann*
Department of Organic Chemistry, Weizmann Institute of Science, RehoVot, Israel, 76100, and
DSM Life Sciences, AdVanced Synthesis and Catalysis, 6160 MD Geleen, The Netherlands
Received February 4, 2003; E-mail: Ronny.Neumann@weizmann.ac.il
The selective oxidation of alcohols to carbonyl compounds is a
key transformation in organic synthesis. Thus, there have been many
recent publications emphasizing environmentally benign methods
using molecular oxygen or hydrogen peroxide as oxidants. The
1
research prior to the year 2000 has recently been reviewed. Since
2
then, in the area of aerobic oxidation, many new homogeneous
3
and heterogeneous catalytic systems have been disclosed. Although
catalytic aerobic oxidation is certainly of importance, there are also
important advantages in the use of aqueous hydrogen peroxide. This
is true especially for smaller scale operations such as in fine
chemicals manufacture, where the complications involving use of
4
oxygen as a gaseous reagent may be avoided. Research involving
catalytic oxidation of alcohols with hydrogen peroxide has been
based either on the use of hydrophobic quaternary ammonium salts
Figure 1. The [WZnM2(H2O)2(ZnW9O34)2]q- polyoxometalate.
5
of molybdenum- and tungsten-containing catalysts or on the use
Table 1. Oxidation of Various Alcohols Catalyzed by
6
Na12[WZnZn2(H2O)2(ZnW9O34)2]a
of manganese or iron complexes with polyamine ligands. These
types of reactions with the catalyst dissolved in the organic phase
inherently require separation of the catalyst from the product,
invariably a chromatographic procedure, for recovery of the catalyst.
A key advance to the area of alcohol oxidation was the finding
that a water-soluble palladium-phenanthroline catalyst may be used
in a biphasic reaction medium that allows liquid alcohols to be
oxidized with water as solvent; the catalyst is easily recycled from
the product by separation of the aqueous phase. Such a system
has the disadvantage that it requires the use of both an expensive
noble metal and a water-soluble organic ligand.
conversion
substrate
mol %
product (selectivity, mol %)
1
-pentanol
66
pentanal (9),
pentanoic acid (91)
2-pentanone (100)
acetone (100)
2-octanone
pentanal (41),
pentanoic acid (59)
benzoic acid (100)
acetophenone (100)
cyclohexanone (100)
cyclooctanone (100)
2-ethyl-3-oxo-1-hexanol (95),
butanoic acid (4)
2-butyl-4-chloro-imidazole-5-
carboxylic acid (100)
1-cyclohexyl-3,3,3-
trifluoro-2-propanone
2-pentanol
2-propanol
94
93
91
62
2
1
-octanol
-pentanolb
7
benzyl alcohol
1-phenylethanol
cyclohexanol
cyclooctanol
∼100
∼100
∼100
95
It would be very advantageous for practical and industrial
applications if a water-soluble catalyst were prepared or “self-
assembled” by simply mixing salts of the required components even
without isolation of the catalyst. Polyoxometalates have recently
been nicely shown by Hill and Weinstock et al. to be amenable to
2
-ethyl-1,3-hexanediol
∼100
2-butyl-4-chloro-5-
hydroxylmethylimidazole
1-cyclohexyl-3,3,3-
trifluoro-2-propanol
>95
8
0
this type of synthesis and use for lignin oxidation. We now report
on the use of easily prepared water-soluble polyoxometalate, Na12
-
9
[WZnZn (H
2 2
O)
2
(ZnW
9
O
34
)
2
], Figure 1, as an effective catalyst in
a
Reaction conditions: 1 mmol of substrate, 5 mmol (∼17 wt %) of
H2O2, 4 µmol of Na12[WZnZn2(H2O)2(ZnW9O34)2], 1 mL of water, 85 °C,
7 h.10 0.012 mmol of TEMPO was added. For more difficult to oxidize
substrates, for example, 2-octanol, a 5-fold molar excess of H2O2 was
needed, but for more active substrates, for example, 1-phenylethanol, a 1.5
molar excess was sufficient. Product distributions were not significantly
affected by carrying out the reactions under Ar.
a biphasic reaction medium with no organic solvent for the selective
oxidation of alcohols with aqueous hydrogen peroxide. Furthermore,
we show that even the nonisolated polyoxometalate prepared in
one step in water from simple salts, and representing a “self-
assembled” catalyst, is equally active for alcohol oxidation.
b
According to the known literature procedure, Na12[WZnZn
O) (ZnW
to a nitric acid solution of sodium tungstate over 5 h at 90 °C.
After isolation, the catalytic activity of Na12[WZnZn (H O)
ZnW
2
-
corresponding ketone in high yields. There is little discernible effect
of the hydrophobicity of the substrate, although not surprisingly
the benzylic substrate was more reactive. A secondary alcohol,
(
H
2
2
O )
9 34 2
] is prepared by dropwise addition of zinc nitrate
9
2
2
2
-
1-cyclohexyl-3,3,3-trifluoro-2-propanol, with a strongly electron-
(
9
O
34
)
2
] for alcohol oxidation was surveyed for a range of
withdrawing CF moiety adjacent to the carbinol center was not
3
substrates, Table 1.
oxidized. Primary alcohols, for example, 1-pentanol and benzyl
alcohol, were oxidized to pentanoic acid and benzoic acid,
respectively. The formation of the carboxylic acid could be partially
inhibited and the oxidation stopped at the aldehyde stage by addition
of catalytic amounts of TEMPO. A 1,3 diol, 2-ethyl-1,3-hexanediol,
was oxidized almost exclusively at the secondary position to yield
Several trends may be noted. First, liquid secondary alcohols
including 2-propanol, 2-pentanol, 2-octanol, 1-phenylethanol, cy-
clohexanol, and cyclooctanol were all selectively oxidized to the
†
Weizmann Institute of Science.
DSM Life Sciences.
‡
5280
9
J. AM. CHEM. SOC. 2003, 125, 5280-5281
10.1021/ja0344821 CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
the appropriate 3-keto alcohol; there was some carbon-carbon bond
cleavage. 2-Butyl-4-chloro-5-hydroxylmethylimidazole, an inter-
mediate for angiotensin II inhibitors,11 also reacted to yield the acid.
This experiment indicates that nitrogen-based moieties, at least for
cases where the nitrogen atom is not susceptible to oxidation, do
not interfere with the catalytic alcohol oxidation.
Acknowledgment. The research was supported by the European
Commission (G1RD-CT-2000-00347) and the Helen and Martin
Kimmel Center for Molecular Design. 2-Butyl-4-chloro-5-hydroxy-
lmethylimidazole, 2-methoxycyclohexanol, and 1-cyclohexyl-3,3,3-
trifluoro-2-propanol were supplied by Mercachem. R.N. is the
Rebecca and Israel Sieff Professor of Organic Chemistry.
The synthesis of the Na12[WZnZn
metalate proceeds according to the following stoichiometry, eq 1.
2 2 2 9 34 2
(H O) (ZnW O ) ] polyoxo-
References
9,12
(
1) Sheldon, R. A.; Arends, I. W. C. E.; Dijksman, A. Catal. Today 2000,
5
7, 157-160.
(2) (a) Steinhoff, B. A.; Fix, S. R.; Stahl, S. S. J. Am. Chem. Sox. 2002, 124,
766-767. (b) Steinhoff, B. A.; Stahl, S. S. Org. Lett. 2002, 4, 4179-
5
Zn(NO ) + 19Na WO + 16HNO f
3 2 2 4 3
4181. (c) Nishimura, T.; Maeda, Y.; Kaikiuchi, N.; Uemura, S. J. Chem.
Na [WZn (H O) (ZnW O ) ] + 26NaNO + 8H O (1)
1
2
3
2
2
9
34 2
3
2
Soc., Perkin Trans. 1 2000, 4301-4305. (d) Hasan, M.; Musawir, M.;
Davey, P. N.; Kozhevnikov, I. V. J. Mol. Catal. 2002, 180, 77-84. (e)
Wolfson, A.; Stijn, S.; de Vos, D. E.; Vankelecom, I. F. J.; Jacobs, P. A.
Tetrahedron Lett. 2002, 43, 8107-8110. (f) Ben-Daniel, R.; Alsters, P.;
Neumann, R. J. Org. Chem. 2001, 66, 8650-8653. (g) Fabbrini, M.; Galli,
C.; Gentilli, P.; Macchitella, D. Tetrahedron Lett. 2001, 42, 4551-4553.
A reaction conducted at 85 °C for 7 h and containing approximately
0 µmol of Na12[WZnZn (H O) (ZnW ] (assuming a theoreti-
4
2
2
2
9 34 2
O )
(
h) Ragagnin, G.; Betzemeier, B.; Quici, S.; Knochel, P. Tetrahedron 2002,
cal 100% yield in the polyoxometalate synthesis) from the solution
obtained in the polyoxometalate preparation, 10 mmol of 2-pentanol,
5
8, 3985-3991. (i) Cecchetto, A.; Fontana, F.; Minisci, F.; Rucupero, F.
Tetrahedron Lett. 2001, 42, 6651-6653. (j) Dijksman, A.; Marino-
Gonzalez, A.; Mairata, I.; Payeras, A.; Arends, I. W. C. E.; Sheldon, R.
A. J. Am. Chem. Soc. 2001, 123, 6826-6833. (k) Iwahama, T.; Yoshino,
Y.; Ketitoku, T.; Sakaguchi, S.; Ishii, Y. J. Org. Chem. 2000, 65, 6502-
and 50 mmol (∼17 wt %) of H
8% yield of 2-pentanone. It should be emphasized that control
reactions at 95 °C, 18 h with (a) no metal catalyst (1 M 2-pentanol,
M H ), (b) only sodium tungstate (1 M 2-pentanol, 0.76 M
Na WO , 5 M H ), (c) only zinc nitrate (1 M 2-pentanol, 0.2 M
Zn(NO , 5 M H ), and (d) a combination of zinc nitrate and
sodium tungstate without addition of nitric acid (1 M 2-pentanol,
.76 M Na WO , 0.2 M Zn(NO , 5 M H ) showed no formation
of 2-pentanone in (a) and (c) and only trace formation, e1%, of
-pentanone in (b) and (d). Therefore, it is clear that only a solution
of Na12[WZnZn (H O) (ZnW ] prepared by “self-assembly”
2 2
O , in 10 mL of water, gave an
8
6
507. (l) Ishii, Y.; Sakaguchi, S.; Iwahama, T. AdV. Synth. Catal. 2001,
43, 393-427. (m) Minisci, F.; Punta, C.; Recupero, F.; Fontana, F.;
3
5
O
2 2
Pedulli, G. F. Chem. Commun. 2002, 688-689. (n) d’Alessandro, N.;
Liberatore, L.; Tonucci, L.; Morvillo, A.; Bressan, M. J. Mol. Catal. 2001,
1
2
4
2 2
O
75, 83-90. (o) Shapley, P. A.; Zhang, N.; Allen, J. L.; Pol, D. H.; Liang,
)
3 2
2
O
2
H.-C. J. Am. Chem. Soc. 2000, 122, 1079-1091. (p) Csjernyik, G.; EÄ ll,
A. H.; Fadini, L.; Pugin, B.; B a¨ ckvall, J. E. J. Org. Chem. 2002, 67, 1657-
1
662.
0
2
4
)
3 2
2 2
O
(
3) (a) Son, Y.-C.; Makwana, V. D.; Howell, A. R.; Suib, S. L. Angew. Chem.,
Int. Ed. 2001, 40, 4280-4283. (b) Makwana, V. D.; Son, Y.-C.; Howell,
A. R.; Suib, S. L. J. Catal. 2002, 210, 46-52. (c) Choudary, B. M.;
Kantam, M. L.; Rahman, A.; Reddy, C. V.; Rao, K. K. Angew. Chem.,
Int. Ed. 2001, 40, 763-766. (d) Mori, K.; Yamaguchi, K.; Hara, T.;
Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Am. Chem. Soc. 2002, 124,
2
2
2
2
9 34 2
O )
of zinc nitrate and sodium tungstate in the presence of nitric acid
was catalytically active.
It is also notable that Na12[WZnZn
to be stable under reaction conditions. Thus, the W NMR of Na12
2 2 2 9 34 2
WZnZn (H O) (ZnW O ) ] shows 10 peaks at δ (ppm) 22.6(1),
11572-11573. (e) Keresszegi, C.; Buergi, T.; Mallat, T.; Baiker, A. J.
Catal. 2002, 211, 244-251. (f) Nishimura, T.; Kakiuchi, N.; Inoue, M.;
Uemura, S. Chem. Commun. 2000, 1245-1246. (g) Kakiuchi, N.;
Nishimura, T.; Inoue, M.; Uemura, S. Bull. Chem. Soc. Jpn. 2001, 74,
165-172. (h) Besson, M.; Gallezot, P. Catal. Today 2000, 57, 127-141.
2 2 2 9 34 2
(H O) (ZnW O ) ] appears
183
-
(
i) Ji, H.; Mizugaki, T.; Ebitani, K.; Kaneda, K. Tetrahedron Lett. 2002,
[
-
-
4
3, 7179-7183. (j) Yamaguchi, K.; Mizuno, N. New J. Chem. 2002, 26,
972-974. (k) Yamaguchi, K.; Mizuno, N. Angew. Chem., Int. Ed. 2002,
538-4540.
4) Sheldon, R. A. J. Chem. Technol. Biotechnol. 1997, 68, 381-388.
(5) (a) Sato, K.; Aoki, M.; Takagi, J.; Noyori, R. J. Am. Chem. Soc. 1997,
16.5(2), -41.6(2), -84.2(2), -89.4(2), -93.8(2), -153.9(2),
4
9
187.3(2), -226.6(2), and -304.7(2) as expected. Upon addition
(
and for at least 12 h, a 10-line slightly shifted 1 W NMR
83
of H O
2 2
1
19, 12386-12387. (b) Bortolini, O.; Conte, V.; Di Furia, F.; Modena,
spectrum is retained, δ (ppm) 22.7(1), -28.2(2), -45.6(2), -93.4-
2), -94.3(2), -96.8(2), -158.4(2), -192.6(2), -231.3(2), and
299.4(2), together with formation of peroxo related peaks at
655.4 and -697.3 ppm. There is no W NMR evidence for
mononuclear tungsten species or peroxotungstate species. Reiso-
G. J. Org. Chem. 1986, 51, 2661-2663. (c) Venturello, C.; Gambaro, M.
J. Org. Chem. 1991, 56, 5924-5931. (d) Ishii, Y.; Yamawaki, K.; Ura,
T.; Yamada, H.; Yoshida, T.; Ogawa, M. J. Org. Chem. 1988, 53, 3587-
(
-
-
3
593. (e) Neumann, R.; Gara, M. J. Am. Chem. Soc. 1995, 117, 5066-
1
83
5074.
(6) (a) Berkessel, A.; Sklorz, C. A. Tetrahedron Lett. 1999, 40, 7965-7968.
13
(b) Brinksma, J.; Rispens, M. T.; Hage, R.; Feringa, B. L. Inorg. Chim.
lation of the Na12[WZnZn (H O) (ZnW ] after completion of
2
2
2
9 34
O )
2
Acta 2002, 337, 75-82. (c) Ligtenbarg, A. G. J.; Oosting, P.; Roelfes,
G.; La Crois, R. M.; Hage, R.; Feringa, B. L.; Lutz, M.; Spek, A. L.
Chem. Commun. 2001, 385-386.
the reaction by evaporation of the water phase showed by IR that
the integrity of the catalyst was retained (peaks at 925, 880, and
(7) (a) ten Brink, G. J.; Arends, I. W. C. E.; Sheldon, R. A. Science 2000,
287, 1636-1639. (b) ten Brink, G. J.; Arends, I. W. C. E.; Sheldon, R.
A. AdV. Synth. Catal. 2002, 344, 355-369.
-
1
7
72 cm ). Furthermore, a catalyst recycle experiment (10 mmol
of 2-pentanol, 50 mmol of H , 40 µmol of Na12[WZnZn (H O)
ZnW ], 10 mL of water, 85 °C, 7 h) carried out simply by
O
2 2
2
2
2
-
(8) Weinstock, I. A.; Barbuzzi, E. M. G.; Wemple, M. W.; Cowan, J. J.;
Reiner, R. S.; Sonnen, D. M.; Heintz, R. A.; Bond, J. S.; Hill, C. L. Nature
(
9 34 2
O )
2001, 414, 191-195.
separation of the organic phase and re-addition of 2-pentanol (10
mmol) and hydrogen peroxide (50 mmol) showed 95%, 90%, and
(9) Tourn e´ , C. M.; Tourn e´ , G. F.; Zonnevijlle, F. J. Chem. Soc., Dalton Trans.
991, 143-151.
1
(
10) Reactions were carried out in 10-25 mL flasks using the conditions
described above. Reactions were quantified by GLC in the presence of
an external standard using a 30 m 5% phenylmethyl silicone capillary
column with an ID of 0.32 mm and 0.25 µm coating, and products were
identified by GC-MS with the same column and conditions.
96% conversions over three reaction cycles with 2-pentanone as
the only product. There was no discernible loss in activity or
selectivity. Eventually, to avoid excess accumulation of water, the
aqueous phase should be concentrated.
We have shown that a water-soluble polyoxometalate is an
effective, stable, and recyclable catalyst for alcohol oxidation with
(
(
11) Binder, D.; Weinberger, J. Eur. Pat. Appl. EP 535420 A1, 1993.
12) The preparation of the polyoxometalate is not affected by the presence of
a substrate (2-pentanol), but addition of H
Na12[WZnZn (H O) (ZnW ].
13) Na WO (δ ) 0 ppm) upon addition of H
2
O
2
prevents the formation of
2
2
2
9 34 2
O )
(
2
4
2
O
2
(0.76 M Na WO , 5 M
2
4
H O
2 2
in biphasic reaction media. The in situ prepared catalyst was
H O ) gave a peak at δ ) -1242 ppm only as expected for tungsten in
2
2
the presence of excess hydrogen peroxide.
as active as the isolated catalyst, while an independent “assembly”
of reaction components was inactive.
JA0344821
J. AM. CHEM. SOC.
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VOL. 125, NO. 18, 2003 5281